332 Miller—The Anatomy of the Heart of Cambarus. 
by all authors which I have consulted, to arise in common with 
the superior abdominal, from a bulbus-like enlargement of the 
posterior end of the heart. This does not hold true for Cam¬ 
barus; the sternal artery is given off as a branch of the superior 
abdominal after it has become established as a distinct artery. 
VALVES. 
Each artery is provided at the point where it leaves the heart 
with valves, which prevent the blood from flowing back into 
the heart. These valves are from 0.25 mm. to 0.5 mm. in 
length. They consist of two loose folds passing parallel to each 
other from one side of the artery to the other; at the junction 
of the artery with the heart these valves are attached to the 
wall of the artery, the free extremity extending into the cavity 
of the artery in the direction of the blood current. 
VALVULAR APERTURES. 
There are no veins entering the heart of the Crayfish, but in 
their place we have six valvular apertures through which the 
blood enters the heart from the pericardial chamber. Two of 
these openings are dorsal and four are lateral. The two dorsal 
apertures are situated well to the anterior of the heart, quite 
near together, separated by the prominent dorsal ridge already 
described. (Pig. 1, PI. V.) They are not placed parallel to the 
long axis of the heart, but they have a forward and outward 
direction, being more closely approximated posteriorly than 
anteriorly. The four lateral apertures are arranged in pairs, 
two on each side. They are, as a rule, situated in the middle 
third; their long axis does not correspond to that of the heart, 
but has a downward and forward direction. I shall call these 
two pair of lateral apertures “ anterior lateral ” and “ posterior 
lateral. ” The posterior lateral apertures are situated in the 
median line on each side, while the anterior lateral apertures 
are situated quite near the ventral border. (Pig. 2, PI. V.) 
Each aperture is provided with valves, as shown in Fig. 7, 
PI. VI, which is a transection of one of the lateral apertures. 
These valves consist of two flaps completely surrounding the 
opening, the free ends of the flaps projecting into the cavity of 
